Bubbles in sucrose and zinc sulphate. Differential interference contrast light micrograph of bubbles in a liquid form of the sugar sucrose, with crystals of zinc sulphate also present. The sucrose has been heated and melted to form a viscous liquid. The fluid flowing around and in the wake of the bubbles is smooth and laminar. Otherwise invisible, the flow is made visible here through a technique called differential interference contrast. Zinc sulphate is used as a dietary supplement to treat zinc deficiency. Magnification: x25 when printed at 10 centimetres tall.